So it's more like a one-time thing, when somebody wins the challenge, the challenge is done. Also if people likes it I plan to make it multi platform, such that you can challenge others even if you don't have your running data on the same platform (strava,garmin etc.)
Yeah that would be interesting feature. An aggregator site, where you can check all your friends runnings. At presents I'm using Strava but some of my friends on Addidas Running and I can't check their progression.